Repairing Tuning String & Guide Wheel

[zorlac]

I received a boombox recently that had a little shipping damage. The tuner string, guide wheel was broken from the plastic peg from where it was attached. The tuner dial was not functioning as result. First thing was rigging a new anchor for the guide wheel. The original was just a plastic peg which was broken flush from the chasis. I drilled it out and used a phono cartridge screw as an anchor. It was perfect size for the guide wheel and a couple washers.

It took a little while to figure out how to reset the tuning string-it only goes on one way. I tried several different combinations with the string until the movement and slack was correct. The hard part was getting the string set over the guide wheel. In order to achieve enough slack you have to expand the spring on the tuning pully.

A couple things before reassembly; calibrate the tuning needle in accordance with the proper station and tuning scale. This is easy as the tuning needle can be adjusted by simply sliding it left or right on the string until it lines up with the scale and proper station. Lastly, clean any finger prints and dust from the tuning scale, tuning needle, glass and all visible parts before reassembling (it sucks going through disassembly and reassembly to realize your tuner window is dirty from the inside-hehe). It's an easy last minute thing before reassembly. Tuner is now functioning properly.

 

[neko]

Great work, i usualy do the same

 

[monchito]

wow zorlac u did an excellent job there .its a shame that they had to make those pegs plastic even thou there are some boxes that use metal pins anyway thanks for sharing ..there is always hope for things like that :monchito:

 

[redbenjoe]

great job --

creative people should rule the world

 

[Fatdog]

I agree with everybody above - great job!

 

[Superduper]

Always great to see a boombox restored to working condition. The feeling of satisfaction must be very gratifying.

One note on the tuner needle thing though. The tuner needle really shouldn't be moved from the factory set position unless the dial is restrung with a brand new cord. The needle/tuning capacitor relationship is critical. Adjustments should always be done "electrically" using factory prescribed adjustments. The reason is that there are high and low calibrations and when the needle is off, it usually means one of the settings has drifted. Merely moving the needle to a new spot might allow the needle to be accurate at, say, 98mhz. But I'll bet that it's probably off further up or down the scale. Usually, the tuning range is adjusted at one extreme, then the other extreme, and back/forth several times. Once the two extremes are calibrated, everything in the middle should line up. Also, while AM and FM shares the same tuning capacitor, the rest of the circuitry (front end) are entirely different. When FM circuitry has drifted, it does not mean AM circuitry has drifted. So moving the needle might fix FM but throw off AM. I understand that sometimes, hiring someone at $75 an hour to adjust the tuner on a $75 boombox isn't economically feasible. I'm just saying that moving the needle is not the recommend procedure for centering the needle since doing it in that way usually only centers it for that one channel.

 

[zorlac]

Thanks for the input guys, it's appreciated. . I agree with "Superduper", messing around with a tuning string the way I have is not recommended. My intensions were to simply change the pin and reassemble the guide wheel. During the repair the tuning string became unraveled. At this point i figured I might as well reasemble the box and just leave the tuner not working as it was.

I was very lucky to get it back in the same position. I started with the tuner all the way to one end and held it in place to reset the string. Usually the tuning needle is fixed on the string and marked. In this situation the needle became loose while fiddling with the mess. I did get very lucky to find it's exact position without having to get it recalibrated electronically. I wouldn't recommend ever touching a tuning cord, it can be a disaster fast. If the string were to break I wouldn't have been as lucky and would have taken it in for restring and calibration.

I am confident of it's functionality now that one of the plastic pins have been replaced. Another point is shipping can be brutal on small plastic pieces which are under tension. These old boomboxes are fun but they are not designed to be bounced around in shipping hehe.